A soft pedal, a pedal that stays down, a creeping vehicle, fluid loss with no drip, and the concentric cylinder nobody wants to quote. What each symptom actually points to.
Clutch hydraulics fail in a small number of recognisable ways, and matching the symptom to the part is the difference between a first-time fix and a three-visit comeback.
The five symptoms
- Pedal slowly sinks to the floor while held — internal bypass past the master cylinder cup seal. The master cylinder is worn; the slave is usually innocent.
- Pedal goes straight to the floor and stays there — a sudden seal failure or a burst hose. Check the slave cylinder and the flexible line together.
- Fluid level drops with no visible puddle — the slave cylinder is often leaking into the bellhousing or the dust boot, where the fluid is absorbed rather than seen.
- Gear engagement gets progressively harder, pedal feels normal — usually a concentric slave cylinder (CSC) losing travel, or air drawn in through a worn seal.
- Pedal feels fine but the clutch slips under load — hydraulic is probably not the fault. Check the friction disc before selling hydraulics.
Why the concentric type is different
A concentric slave cylinder sits inside the gearbox on the input shaft and acts directly on the release bearing. It has no external linkage and no adjustment, which makes it reliable but unforgiving: it cannot be bled by pumping the pedal alone, and it must be replaced as a complete assembly. Workshops often try to sell the cheaper external part on a vehicle that was built with a CSC — which is a guaranteed comeback.
What to stock
For a general aftermarket market, stock the clutch master and the external slave for your top-selling models as a matched pair, and hold the CSC numbers on request rather than on the shelf. The CSC is a lower-volume, higher-value line — worth quoting, not worth blocking cash on.
Always sell the master and slave together when the system is more than a few years old. Contaminated fluid from a failing seal on one end is the fastest way to destroy the new part you just fitted on the other.